Treatment of hydrocarbons



Patented Mar. 14,1944

TREATMENT OF HYDROCAEBONS William J. Mattox, Chicago, 111., assignor toUniversal -il Products Company, Chicago, corporation of Delaware NoDrawing. Application December 28, 1939. Serial No. 311,306

8 Glaims.

This invention relates particularly to the conversion of straight chainhydrocarbons into closed chain or cyclic hydrocarbons.

More specifically it is concerned with a proccss involving the use ofparticular catalysts and specific conditions of operation in regard totemperature, pressure, and time of reaction whereby aliphatichydrocarbons can be converted efii-e ciently into aromatic hydrocarbons.

In the straight pyrolysis of pure hydrocarbons or hydrocarbon mixtures,such as those encountered in fractions from petroleum or those occurringnaturally or produced synthetically, the reactions involved whichproduce aromatics from paramns and olefins are of a complicatedcharacter and are diflicult'to control.

The search for catalysts to specifically control and accelerate desiredconversion reactions amonghydrocarbons has been attended with the usualdifilculties encountered in finding catalysts for other types ofreactions since there are no basic laws or rules for predicting theefiectiveness of catalytic materials and the art as a whole is in a moreor less empirical state. In using catalysts even in connection withconversion reactions among pure hydrocarbons and particularly inconnection with the conversion of the relatively heavy distillatesand-residua which are available for cracking; there is a generaltendency for the decomposition reactions to proceed at a very rapidrate, necessitating the use of extremely short time factors and veryaccurate control of temperature and pressure to avoid too extensivedecomposition. ,There are further dimculties encountered in maintainingthe ciliciency of catalysts employed in pyrolysis since there is usuallya rapid deposition of carbonaceous materials on their surfaces and intheir pores.

The foregoing brief review of the art of hydrocarbon pyrolysis is givento furnish a general background for indicating the improvement in suchprocesses which is embodied in the presentinvention, which may beapplied to the treatment of pure paraflin or olefin hydrocarbons;hydrocarbon mixtures containing substantial per centages of paraffinhydrocarbons such as relatively close out fractions producible bydistilling petroleum, and analogous fractions which con tain unsaturatedas well as saturated straight chain hydrocarbons, such fractionsresulting from cracking operations upon the heavier fractions ofpetroleum.

In one specific embodiment the present invention comprises a process torproducing aromatic reactions involving dehydrogenation, cyclization.

ing essentially a major proportion of thorium r ng closure with theproduction in the simplest oxide and a relatively minor proportion of onides of elements selected from the members of the left-hand columnsofgroups 5 and 6 of the periodic table. I

According to the present invention aliphatic or straight chainhydrocarbons having 6 or more carbon atoms in chain arrangement in theirstructure are specifically dehydrogenated in such a way that the chainof carbon atoms undergoes case of benzene from n-hexane or n-hexene andin the case of higher molecular weight parafiins of various alkylderivatives of benzene. Under properly controlled .conditions oftemperature, pressure, and time of contact, very high yields of theorder of '75 to of the benzene or aromatic compounds are obtainablewhich are far in excess of any previously obtained in the art eitherwith or without catalysts. For the sake of illustrating and exemplifyingthe types of hydrocarbon conversion reactions which are specificallyaccelerated under the preferred conditionsby the present types ofcatalysts, the following structural equations are introduced:

fi fig on, on. on on H 4H2 CH1 CH1 CH CH n-Hcxane Benzene on, c-cHi 0H,CHr-CH: CH OH I 'II' 43: H: CH: H CH C a CH n-Heptane Toluene C31 /CHon, CHr-CH: CH f-cu: m

l H: QHlr-CH: H C-CH:

7 CH C n-Octanc o-Xylcnc Ethyl benzene and m-xylene and p-xylene arealso formed from n-octane by a. combination of and isomerization, but noidea is oiiered as to the probable order in which these reactions occur.

In the foregoing table the structural formula of each of the primaryparafiin hydrocarbons has been represented as a nearly closed ringinstead of by the usual linear arrangement for the sake of indicatingthe possible mechanisms involved. No attempt has been made to indicatethe possible intermediate existence of mono-olefins, dioleflns,hexarnethylenes or'alkylated hexamethylenes which might result from theloss of various amounts of hydrogen. It is not known at the present timewhether ring closure occurs at the loss of one hydrogen molecule orwhether dehydrogenation of the chain carbons occurs so that the firstring compound formed is an aromatic such as benzene or one of itsderivatives. The above three equations are of a relatively simplecharacter indicating generally the type of reactions involved but in thecase of n-paraiiins or mono-olefins of higher molecular weight than theoctane shown and in the case of branch chain compounds which containvarious alkyl substituent groups in different positions along theG-carbon atom chain, more complicated reactions will be involved. Forexample, in the case of such a primary compound as '2,3-dimethyl hexanethe principal resultant product is apparently o-xylene although thereare concurrently produced definite yields of such compounds as ethylbenzene indicating an isomerization of two substituent methyl groups. Inthe case of nonanes which are represented by the compound2,3,4-trimethyl hexanefithere is formation not only of mesitylene butalso of such compounds as methyl ethyl benzene and various propylbenzenes.

It will be seen from the foregoing that the scope of the presentinvention is preferably limited to the treatment of aliphatichydrocarbons which contain at least 6 carbon atoms in straight chainarrangement. In the case of paraflin hydrocarbons containing less thanG-carbon atoms in linear arrangement, some formation of aromatics maytake place due to primary isomerization re- I actions although obviouslythe extent of these will vary considerably with the type of compound andthe conditions of operation. The process is readily applicable toparamns from hexane up to dodecane and their corresponding olefins. Withincrease in molecular weight beyond this point the percentage ofundesirable side reactions tends to increase and yields of the desiredalkylated aromatics decrease in proportion.

The thorium oxide carrier referred to above has a relatively lowdehydrogenating activity, while the oxides of the elements mentioned areof relatively high catalytic activity and furnish by far the greaterproportion of the observed catalytic eflects. The oxides of theseseveral elements vary somewhat in catalytic activity in any givenreaction comprised within the scope of the invention and this variationwill be greater in the case of different types of dehydrogenation andisomerization reactions.

In regard to the preparation of thoria employed as a carrier or supportfor the preparation of dehydrocyclization catalyst, it may be statedthat thoria may be obtained by known methods from a number of mineralsincluding thorite, orangite, and thorianite.

The catalytic dehydrogenating efiiciency of thorium is greatly improvedby the presence of oxides of the preferred elements in relatively minoramounts. The oxides which constitute the principal active catalyticmaterials-may be deposited upon the surface and in the pores of stantlysince the observed catalytic effects evidently' depend principally onsurface action.

The oxide of vanadium which results from ignition of the nitrate, thehydroxide, or the carbonate is principally the pentoxide V205 which isreduced by hydrogen to form thetetroxide V204; or the correspondingdioxide V02 and then to the sesquioxide V203. In any case the primarydeposition of vanadium compounds upon thoria granules may be made by theuse of the soluble vanadyl sulfate or the nitrate and also solutions ofammonium and alkali metal vanadates may be employed, which furnishalkaline residues on ignition. It is probable that the sesquioxide 'isthe principal compound which accounts for the catalytic activityobserved with vanadium catalysts in reactions of the present character.

Columbium has several oxides which may be employed as catalyst;components supported by thoria although the lower oxides are most like-.

iv to exist under the conditions employed in the process. The pentoxideCbzOs results from the ignition of the pentahydroxidewhich may beprecipitated from solutions of soluble compounds such as the mixedfluoride of columbium and potassium. Solutions of alkali metalcolumbates may also be employed as a source of catalytic material, thesefurnishing an alkaline residue on drying and ignition. The pentoxide isdefinitely reduced by hydrogen or by hydrocarbons at the preferredtemperatures of operation so that the essential catalysts for the majorproportion of a run will probably include the lower oxides CbOz. ch20:and C110.

Th element tantalum which has the highest atomic number of the fifthgroup of elements herein mentioned, also has the pentoxide TazOs, atetroxide TazOq and probably a sesquioxide TazOa. The higher oxide isprepared by the ignition of the precipitated pentahydro'xideprecipitated from soluble salts. The element chromium has three oxides,the trioxide CrOa, the dioxide CrOz, and the sesquioxide ClzOs, the lastnamed being readily produced by heating the trioxide in hydrogen orhydrocarbon vapors at a temperature of 250 C. The dioxide has beenconsidered to be an equimolecular mixture of the trioxide and thesesquioxide. The oxides are readily, developed on the surface and in thepores of thoria granule by utilizing primary solutions of chromic acidH2Cl04 or chromium nitrate Cr(NOa)a. The isnition of the chromicacid,the nitrate, or the precipitated trihydroxide produces primarilythe trioxide which is then reduced to the sesquioxide to furnish anactive catalyst for use in reactions of the present character.

The two most important oxides of molybdenum which are employedalternatively in the production of dehydrocyclization catalysts,according to the present invention, are the dioxide M002, and thesesquioxide M0203. Since thereduction of the trioxide by hydrogen beginsat about 300 C. and the reduction is rapid at 450 just requisite to wetthe carrier-granules uniformly and the mass is then dried and calcined.

The element tungsten has three oxides: the trioxide W02, the dioxideW02, and the sesquioxide W203. The trioxide is readily soluble inaqueous ammonia from which it may be deposit- I ed upon thoria. granulesand it is ordinarily re duccd preliminary to service by the action ofhydrogen at a relatively high temperature. Tungstic acids may beprecipitated from the hydrated oxides and these may be heated to driveofi water and leave a residue of oxides on the carrier particles. I

In regard to uranium, which i the heaviest member of the present naturalgroup of elements whose oxides are preferred as catalysts. it may merelybe stated that while this element furnishes catalytic oxides having someorder of catalytic activity, its scarcity and cost naturally preeludeits extensive use in practice.

It has been found essential in the production of high yields ofaromatics from parafilnic hydrocar-bons when using the preferred'typesof dehydrocyclization catalysts that, depending upon the parafilnichydrocarbon or mixture of hydrocarbons being treated, temperatures from450 to 650 C. should be employed, contact times of approximately 0.1-60seconds, and pressures approximating atmospheric. The use ofsubatmospheric pressure of the order of /4 atmos-- phere maybe-beneflcial in that reduced pressure generally favors selectivedehydrogenation reactions, but on the other hand moderatelysuperatmospheric pressure, usually of the order of less than 100 poundsper square inch, increases the capacity of commercial plant equipment,so

that in practice a balance is struck between these two factors.

While the present process .is particularly applicable to the productionof the corresponding aromatics from an aliphatic hydrocarbon or amixture of aliphatic hydrocarbons the invention may be employed also toproduce aromatics from olefinic hydrocarbon mixtures such as distillatesfrom paraflinic or mixed-base crude petroleum. In this case the aromaticcharacter of the distillate will be increased and as a rule the octanenumber of theproduct will be higher than that of the charging stock. Ifdesired and found feasible on a basis of concentration, the aromaticsproduced in the hydrocarbon mixtures may be recovered as such bydistillation to fractions of proper boiling range followed by chemicaltreatment with reagents capable of reacting selectively with them.Another method for concentrating aromatics will involve the use ofselective sclvents such as liquid sulfur dioxide, furfural, chlorex, andalcohols.

to further contact with the dehydrocyclization catalyst so as to convertthese olefins into further quantities of aromatics and form asubstantially olefin-free aromatic product.

These catalysts consisting of thoria activated by oxides of the elementsof the left-hand columns of groups 5 and 6-0f the periodic table may becomposited with stabilizing oxides such as magnesium oxide to produce acatalyst composite which retains its aromatic-forming activity aftermany periods of use and reactivation by burning off carbonaceousdeposits in an oxygen-contaming atmosphere. Composites of thoria andactivating metal oxides such as are hereinabove described efiect arelatively high conversion of The process of this invention makespossible the production of aromatic concentrates or aromaltic-paraffinichydrocarbon mixtures which are free from olefins and suitable forsolvent extraction or other methods of separating pure aromatics, orwhich may be used directly for nitration Or for other chemical reactionsto which the presence of olefins would be objectionable. By this processthe olefins formed incidental to the CYOliZflltiOn reaction areconverted into aromatics thereby increasing further the yield of thesedesirable hydrocarbons.

The following example is introduced to show results obtainable in theoperation of the process,

although these data are not presented with the intention of undulylimiting the broad scope of the-invention:

EXAMPLE A catalystcontaining 8% by weight of chroamnic fraction iscontacted, for example, with a material comprising granular activatedthoria.

supporting 432% by weight of chromium sesquioxide. The'cyclicizedmaterial containing relatively small amounts of olefins may be recycledoxide was prepared b dissolving 84.2 parts by weight of crystallinechromic nitrate,

Cr (N03) 3.9H2O

and 385 parts by weight of thorium nitrate, Th(NO3)4.4H2O, in 8000 partsby weight of water, followed by precipitating the hydrated oxides byaddition of 225 parts by weight of concentrated ammonium hydroxidesolution. The precipitates were removed from the solution by filtration,wased with distilled water, dried at -200 0;, then pressed into cakes ona hydraulic press, and later broken and sized to produce 10-12 meshparticles which were calcined in a stream of dry air at 550 C. for onehour.

This granular calcined catalyst was employed as a filler in a tubethrough which normal heptane was passed at 550 C. at a charging ratecorresponding to an hourly liquid space velocity of 2. Table 1 givesresults obtained on normal heptane in the presence of the abovedescribed catalyst consisting of approximately 8% chromium sesquioxideand 92% thoria.

TABLE 1 Cycliaation of normal heptane in the presence of 8% chromiumsesquioride and 92% thoria Yields, weight per cent of charge:

Total hydrocarbon 93.2 Toluene 24.2 Carbon a- 1.9 Gas, uncondensed 6.8

Yields, weight per cent of heptane decomposed:

Toluene 78.2

Gas 21.

Composition of hydrocarbon recovery, weight The results given in Table 1show that a relatively high per cent of the heptane decomposed wasconverted into toluene in the presence of the chromiumsesquioxide-thoria catalyst, the yields of toluene per pass being of theorder of 26% by weight of the charge.

Th foregoing specification and example show clearly the character of theinvention and the results to be expected in its application to aliphatichydrocarbons including paraflins and olefins, although neither sectionis intended to unduly limit its generally broad scope.

I claim as my invention:

1. A process for producing aromatic hydrocarbons from aliphatichydrocarbons containing at least six carbon atoms in straight chainarrangement which comprises dehydrogenating and cyclicizing saidaliphatic hydrocarbons under dehydrocyclization conditions oftemperature and pressure in the presence of a dehydrocyclizationcatalyst comprising essentially a major proportion of thorium oxide andrelatively minor proportions or magnesium oxide and an oxide of anelement selected from the members of the lefthand column of group 6 ofthe periodic table.

2. A process for producing aromatic hydrocarbons from aliphatichydrocarbons containing straight chains of 6-12 carbon atoms permolecule which comprises dehydrogenating and cyclicizing said aliphatichydrocarbons under dehydrocyclization conditions of temperature andpressure in the presence of a dehydrocyclization catalyst comprisingessentially a major proportion of thorium oxide andv relatively minorproportions oi magnesium oxide and an oxide oi an element selected fromthe members or the left-hand column of group 6 of the periodic table.

3. A process for producing aromatic hydrocarbons from aliphatichydrocarbons containing straight chains of 6-12 carbon" atoms permolecule which comprises dehydrogenating and cyclicizing said aliphatichydrocarbons at a temperature of the order of 450-650 C. in the presenceof a dehydrocyclization catalyst comprisingessentially a majorproportion oi! thorium oxide and relatively minor proportions ofmagnesium oxide and an oxide of an element selected from the members ofthe left-hand column of group 6 or the periodic table.

' 4. A process for producing aromatic hydrocarbons from aliphatichydrocarbons containing straight chains of 6-12 carbon atoms permolecule which comprises dehydrogenating and cyclicizing said aliphatichydrocarbons at a temperature of the order of 450-650 C. under apressure in the range of substantially atmospheric to approximately 100pounds per square inch'in the presence of a dehydrocyclization catalystcomprising essentially a major proportion of th rium oxide andrelatively minor proportions of mag:

nesium oxide and an oxide of an element selected 6 from the members ofthe left-hand column of group 6 of the periodic table.

5. A process for producing aromatic hydrocarbons from aliphatichydrocarbons containing straight chains of 6-12 carbon atoms per molelcule which comprises dehydrogenating and cyclicizing said aliphatichydrocarbons at a temperature of the order of 450-650 C. undera-pressure in the range of substantially atmospheric to approximately100 pounds per square inch for an is average time of contact ofapproximately 0.1-60 seconds in the presence of a dehydrocyclizationcatalyst comprising essentially a major proportion of thorium oxide andrelatively minor proportions of magnesium oxide and an oxide of anelement selected from the members of the lefthand column of group 6 oftheperiodic table consisting of chromium, molybdenum, tungsten, anduranium.

6. A process for producing aromatic hydrocar- 26 bons from aliphatichydrocarbons containing straight chains of 6-12 carbon atoms permolecule which comprises dehydrogenating and cyclicizing said aliphatichydrocarbons at a temperature of the order of 450-650 C. under apressure in'the range of substantially atmospheric to approximately 100pounds per. square inch for an average time oi contact of approximately0.1-60 seconds in the presence of a dehydrocyclization catalystcomprising essentially a major proportion of thorium oxide andrelatively'minor proportions of magnesium oxide and an oxide ofchromium. 7. A process for producing aromatic hydrocarbons fromaliphatic hydrocarbons containing straight chains of- 6- 2 carbon atomsper molecule which comprises dehydrogenating and cyclicizing saidaliphatic hydrocarbons at a temperature of the order of 450-650 C. undera pressure in the range of substantially atmospheric to approximately100 pounds per square inch for an average time of contact ofapproximately 0.1-

60 seconds in the presence 01 a dehydrocyclization catalyst comprisingessentially a major pro-' portion of thorium oxide and relatively minorproportions of magnesium oxide and an oxide of molybdenum.

8. A process for producing aromatic hydrocarbons irom aliphatichydrocarbons containing straight chains 01' 6-12 carbon atoms permolecule which comprises dehydrogenating and cyclicizing said aliphatichydrocarbons at a temperature of the order of 450-650 C. under apressure in the range of substantially atmospheric to approximately 100pounds per square inch for an average time 01' contact of approximately0.1-60 seconds in the presence of a dehydrocyclization catalystcomprising essentially a major proportion of thorium oxide andrelatively minor proportions of magnesium oxide and an oxide or anelement selected from the members 01 the lefthand column of group 6 ofthe periodic table consisting or chromium, molybdenum, tungsten'anduranium.

WILLIAM J. MA'I'IOX.

